linux-kernel - Re: [PATCH v2 1/1] mm/vmscan.c: Prevent allocating shrinker

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Date:   Mon, 13 Dec 2021 11:10:31 -0800
From:   Yang Shi <shy828301@...il.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Nico Pache <npache@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>,
        Vladimir Davydov <vdavydov.dev@...il.com>, raquini@...hat.com,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v2 1/1] mm/vmscan.c: Prevent allocating shrinker_info on
 offlined nodes

On Tue, Dec 7, 2021 at 11:59 PM Michal Hocko <mhocko@...e.com> wrote:
>
> On Tue 07-12-21 17:26:32, Yang Shi wrote:
> > On Tue, Dec 7, 2021 at 5:23 PM Yang Shi <shy828301@...il.com> wrote:
> > >
> > > On Tue, Dec 7, 2021 at 4:33 PM Nico Pache <npache@...hat.com> wrote:
> > > >
> > > >
> > > >
> > > > On 12/7/21 19:26, Yang Shi wrote:
> [...]
> > > > > AFAICT, we have not reached agreement on how to fix it yet. I saw 3
> > > > > proposals at least:
> > > > >
> > > > > 1. From Michal, allocate node data for all possible nodes.
> > > > > https://lore.kernel.org/all/Ya89aqij6nMwJrIZ@dhcp22.suse.cz/T/#u
> > > > >
> > > > > 2. What this patch does. Proposed originally from
> > > > > https://lore.kernel.org/all/20211108202325.20304-1-amakhalov@vmware.com/T/#u
> > > >
> > > > Correct me if im wrong, but isn't that a different caller? This patch fixes the
> > > > issue in expand_one_shrinker_info.
> > >
> > > Yes, different caller, but same approach. The cons with this approach
> >
> > And the same underlying problem.
> >
> > > is we have to fix all the places. It seems Michal and David are not
> > > fans for this approach IIRC.
>
> Yes, agreed. We definitely do not want to spread this node_offline
> oddity all over the place. There are two different way to approach this.
> Either we handle node_offline nodes at the page allocator level when
> setting the proper zonelist (ideally protect that by a static key for
> setups which have these nodes) or we allocate pgdat for all possible
> nodes. I would prefer the second because that is more robust (less
> likely to blow up when somebody does
>         for_each_node(nid)
>                 something(NODE_DATA(nid))
>
> The discussion is ongoing at the original thread where Alexey Makhalov
> reported a similar problem (the subthread is
> http://lkml.kernel.org/r/Ya89aqij6nMwJrIZ@dhcp22.suse.cz)

Thanks, Michal. Yeah, it seems more straightforward and more robust to
me. I'm not familiar with memory hotplug, hopefully it doesn't break
hotplug.

> --
> Michal Hocko
> SUSE Labs